Recently, there is a growing demand for solar cells that have been noticed as energy supplying means alternative to petroleum which is a cause of global warming. With the increase in demand for solar cells, stable supply and cost reduction of parts such as back sheets for solar cells have been required, and also there is a growing demand for improving power generation efficiency of solar cells.
Back sheets for solar cells are layered on an encapsulating resin face after encapsulating a silicon cell under the glass plate with the encapsulating resin such as ethylene vinyl acetate resin.
Conventionally, as the back sheet for solar cells, a white thermoplastic resin sheet layered on both faces of a polyester sheet has been used in order to improve reflection of sunlight so as to improve power generation efficiency of solar cells (Patent Documents 1 and 2).
On the other hand, since solar cells are arranged on a house roof, back sheets for solar cells colored in dark colors such as black have been recently required from the viewpoint of design.
However, the conventional black back sheet for solar cells is generally molded by kneading a carbon black into a resin, and thus the carbon black absorbs sunlight and increases the temperature. As a result, power generation efficiency of solar cells is lowered, and durability may also be lowered.
On the other hand, a back sheet for solar cells with low heat storage, which is obtained by kneading an inorganic pigment having an infrared reflecting property in a rubber-reinforced vinyl resin followed by molding, has been also suggested (Patent Document 3), but further improvement in infrared reflectivity has been required.
In addition, a back sheet for solar cells provided on a surface thereof with a black resin layer containing a perylene pigment and having a light reflectance at a wavelength of 800 to 1100 nm of 30% or higher so as to reflect near-infrared light and prevent heat storage is also proposed (Patent Document 4), but since the substrate thereof is made of a polyethylene terephthalate film, it is inferior in weatherability and hydrolytic resistance disadvantageously.
Moreover, since the back sheet is layered on an encapsulating resin surface of solar cells as mentioned above, it is required to have a water vapor barrier property in order to prevent vapor from invading the encapsulating resin from the back sheet and deteriorating silicone cells.    Patent Document 1: Japanese Patent Laid-open No. 2006-270025    Patent Document 2: Japanese Patent Laid-open No. 2007-177136    Patent Document 3: Japanese Patent Laid-open No. 2007-103813    Patent Document 4: Japanese Patent Laid-open No. 2007-128943